The present invention relates to a network management system in which network stations connected to a network are managed by a network management station, and in particular, to a network management method in which a power-off operation of a network station is monitored by the network management station.
There has been known a conventional technology of managing a network in which a network management station issues at a fixed interval inquiries to network stations for such information as operational states and failures thereof such that each network station sends a response to the network management station.
The prior art is achieved on assumption that the network stations are kept powered and are normally operating in any situation. When a failure occurs in a data line, the inquiry from the network management station to each network station as well as the response from the network station to the network management station cannot be normally achieved. The network management station therefore notifies that communications between the network management station and the network stations have been interrupted.
Due to the assumption that the network stations are kept powered in the system operation, there has been a problem that when the network management station notifies the interruption of communication as above, it is impossible to decide whether there occurred a failure in the data line or a power-off operation in a network station.
A technology of notifying the power-off of a network station has been described in the JP-A-2-283141. However, a function to identify a partner to which the notification is to be sent is missing in this technology, this consequently leads to a problem that it cannot be guaranteed that the event of power-off is actually notified to a desired destination. According to the prior art, in a network having a complex structure, a broadcast message of a power-off event is transmitted to all terminals in the network. This is associated with a problem of increase in traffic load imposed on the network.
As described above, the conventional technology is attended with a problem that the network management station cannot discriminate between an event that a network station connected to the network cannot achieve communication due to a failure of a data line and an event that the interruption of communication is caused because the network station is turned off.
Particularly, in a system including a public or global network, when the network is managed by a particular network management station, there arises a problem. Namely, to achieve notification of the power-off event, each network station is required to have a function to identify the network management station.